The type 2 deiodinase (D2) activates thyroid hormone and constitutes an important source of 3,5,3 ,-triiodothyronine in the brain. D2 is inactivated via WSB-1 mediated ubiquitina- tion but can be rescued from proteasomal degradation by USP-33 mediated deubiquitination. Using an in silico analysis of published array data, we found a significant positive cor- relation between the relative mRNA expression levels of WSB-1 and USP-33 in a set of 56 mouse tissues (r 0.08; P < 0.04). Subsequently, we used in situ hybridization combined with immunocytochemistry in rat brain to show that in ad- dition to neurons, WSB-1 and USP-33 are differently ex- pressed in astrocytes and tanycytes, the two main D2 express- ing cell types in this tissue. Tanycytes, which are thought to participate in the feedback regulation of TRH neurons ex- press both WSB-1 and USP-33, indicating the potential for D2 ubiquitination and deubiquitination in these cells. Notably only WSB-1 is expressed in glial fibrillary acidic protein-pos- itive astrocytes throughout the brain. Although developmen- tal and environmental signals are known to regulate the ex- pression of WSB-1 and USP-33 in other tissues, our real-time PCR studies indicate that changes in thyroid status do not affect the expression of these genes in several rat brain re- gions, whereas in the mediobasal hypothalamus, changes in gene expression were minimal. In conclusion, the correlation between the relative mRNA levels of WSB-1 and USP-33 in numerous tissues that do not express D2 suggests that these ubiquitin-related enzymes share additional substrates be- sides D2. Furthermore, the data indicate that changes in WSB-1 and USP-33 expression are not part of the brain ho- meostatic response to hypothyroidism or hyperthyroidism.

Expression Patterns of WSB-1 and USP-33 Underlie Cell-Specific Posttranslational Control of Type 2 Deiodinase in the Rat Brain.

Csaba Fekete, Beatriz C. G. Freitas, Aniko ́ Zeo ̈ld, Ga ́bor Wittmann, Andrea Ka ́da ́r, Zsolt Liposits, Marcelo A. Christoffolete, Praful Singru, Ronald M. Lechan, Antonio C. Bianco, and Bala ́zs Gereben. Endocrinology. May 8, 2008. doi: 10.1210/en.2007-0448

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